Temperature dependent fabrication of various rod and rhombohedral-shaped mesoporous Co3O4 crystals and their capability towards elimination of toxic Cr(vi) ions from the aquatic environment

Abstract

Currently, wastewater treatment is a vital environmental concern as it is a huge challenge for people to live healthy lives. Consequently, legislation aimed at ensuring the removal of toxic effluents from wastewater is becoming increasingly stringent, making the development of more efficient nanomaterials that can safely degrade toxic effluents a crucial challenge for chemists in the 21st century. Despite widespread investigations to this topic, the design of an efficient system remains a key challenge. Herein we advance the prior art by designing phase pure mesoporous Co₃O₄ through a simple co-precipitation method followed by annealing. Mesoporous cylindrical rods and non-porous rhombohedral shaped Co₃O₄ crystals are structured at lower and higher annealing temperatures, respectively. The as-synthesized Co₃O₄ is subjected to several microscopic and spectroscopic analyses. The XRD and SAED patterns and XPS studies verified the creation of the cubic phase and TEM analysis substantiated the formation of cylindrical rod and rhombohedral shaped Co₃O₄ crystals. The as-designed rod-shaped Co₃O₄ crystals show much higher adsorption capacity (>127 mg g⁻¹), uptake capacity and Cr(VI) removal efficiency (∼93%) at a neutral pH compared to their higher temperature analogues. The as-synthesized materials were applied for the successful degradation of Cr(VI) ions and the results were compared with the results of other literature reports. From recyclability tests, we confirmed that the most efficient catalyst can be straightforwardly collected after the reaction and can be reused several times with a negligible loss of catalytic efficiency. By adjusting different reaction parameters such as pH and the concentration of the adsorbent and adsorbate, the adsorption properties of the catalyst can be controlled. With the help of some theoretical models which are based on kinetic and equilibrium data, a feasible mechanism for the Cr(VI) removal process using Co₃O₄ is also suggested.